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Iron and callose homeostatic regulation in rice roots under low phosphorus
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Section of Biology | Faculty of Science of the University of Geneva
Pop-up div Successfully Displayed This div only appears when the trigger link is hovered over. Please Wait. Two of the most commonly encountered causes of low bone mass— osteoporosis and osteomalacia —are reviewed, along with discussions regarding their pathogenesis. Normal parathyroid glands each weigh 30—40 mg and are gray-tan to yellow-gray. Each individual typically has four glands, so that the average total parathyroid tissue mass in the adult is — mg. The superior pair of parathyroid glands arise from the fourth branchial pouches in the embryo.
These glands are located near the point of intersection of the middle thyroid artery and the recurrent laryngeal nerve. The superior parathyroid glands may be attached to the thyroid capsule posteriorly or, rarely, embedded in the thyroid gland itself. Alternative locations include the tracheoesophageal groove and the retroesophageal space. The blood supply to the superior parathyroid glands is from the inferior thyroid artery or, less commonly, the superior thyroid artery.
Normal Regulation of Calcium & Phosphorus Metabolism
The inferior parathyroid glands develop from the third branchial pouch, as does the thymus gland. These glands typically lie at or near the lower pole of the thyroid gland lateral to the trachea. The inferior glands receive their blood supply from the inferior thyroid arteries. The location of the inferior parathyroid glands is variable. When there are ectopic glands, they are typically found in association with thymic remnants.
A common site for ectopic glands is the anterior mediastinum. Less common ectopic locations are the carotid sheath, pericardium, and pharyngeal submucosa. This becomes a critically important issue when such ectopic glands develop hyperparathyroidism. The parathyroid gland is composed of three different cell types: chief cells, clear cells, and oxyphil cells. In their active state, they have a prominent endoplasmic reticulum and dense Golgi regions where PTH is synthesized and packaged for secretion.
Clear cells are probably chief cells with an increased glycogen content. Oxyphil cells appear in the parathyroid glands after puberty. Aim: This study was undertaken to examine the effects of long-term vitamin D treatment on calcium, phosphate and magnesium homeostasis at organ level in hypoparathyroid patients. Methods: Fifteen vitamin D-treated hypoparathyroid patients were studied, eight of the patients in a combined 47 Ca kinetic and calcium, phosphate and magnesium balance study.
Results were compared with a matched control group of 12 normal individuals. Results: All the patients had normal serum levels of calcium, phosphate and magnesium.
Twenty-four-hour urinary hydroxyproline excretion and serum cross-linked carboxyterminal telopeptide of type I were in the upper normal range. All parameters from phosphate homeostasis were normal. Conclusion: Long-term vitamin D treatment in hypoparathyroid patients resulted in a positive calcium balance.